1. Technical Field
The present invention relates to a structure of a spring and an actuator using this spring. Specifically, the present invention relates to a structure of a spring in a leaf spring shape, and an actuator such as a relay or a mirror device using this spring.
2. Related Art
To date, various structures have been proposed as a small sized actuator, in particular, an MEMS (Micro-Electro Mechanical System) device, using a leaf spring.
(Japanese Unexamined Patent Publication No. 2002-326197)
For example, according to an MEMS device described in Japanese Unexamined Patent Publication No. 2002-326197, two signal lines are disposed on a substrate so that ends of the signal lines face each other, and fixed electrodes are provided on both sides of the signal lines so as to sandwich both the signal lines. Further, a drive electrode faces so as to face each fixed electrode above the substrate, and a contact portion (contact switching portion) provided between the both drive electrodes faces the each end of the both signal lines (contact pair) so as to be able to be in contact with and separated from the ends of the both signal lines. The drive electrode and the contact portion are elastically supported above the substrate by a spring.
According to this MEMS device, when closing between the signal lines to permit conduction, an electrostatic attractive force is produced between the drive electrode and the fixed electrode and the drive electrode is attracted to the fixed electrode, thereby bringing the contact portion into electrical contact with each end of the both signal lines.
However, according to the structure shown in Japanese Unexamined Patent Publication No. 2002-326197, only a single pair of contact pair can be switched, and a c contact structure cannot be adopted. Specifically, it is not possible to provide a structure including a common contact (c contact) and a pair of contacts (a contact and b contact), and in which switching between the a contact and the c contact and switching between the b contact and the c contact are alternately carried out.
(Japanese Unexamined Patent Publication No. 2006-190594)
A micro contact switching device disclosed in Japanese Unexamined Patent Publication No. 2006-190594 is able to carry out switching of a plurality of pairs of contact pair. Specifically, according to the micro contact switching device described in Japanese Unexamined Patent Publication No. 2006-190594, a center of a band plate-shaped flexible micro movable portion is unfixedly supported by a fulcrum portion, and an upper electrode that faces a lower electrode on the substrate and a moving contact that faces a pair of fixed contacts (fixed contact pair) on the substrate are respectively provided on both end portions of the micro movable portion.
This micro contact switching device has a structure such that, a voltage to one of the upper electrode and the lower electrode is applied to cause the both electrodes to be attracted to each other, and the micro movable portion is caused to be inclined or flexed, and thereby bringing the moving contact that is close to the electrodes into contact with the fixed contact pair.
According to the micro contact switching device of this structure, it is possible to provide the structure as the c contact structure by electrically connecting one fixed contact of one fixed contact pair and one fixed contact of the other fixed contact pair by wiring.
However, according to the micro contact switching device disclosed in Japanese Unexamined Patent Publication No. 2006-190594, the following action is carried out to switch the fixed contact pairs on the right and left. For example, a case is assumed in which the upper electrode and the lower electrode on the right side are attracted and the moving contact on the right side is in contact with the fixed contact pair, thereby closing between the fixed contact pair. When the switch of the fixed contact pair is switched in this state, it is required that the attraction between the upper electrode and the lower electrode on the right side is released and then the moving contact on the right side is separated from the fixed contact pair, and the upper electrode and the lower electrode on the left side are attracted and the moving contact on the left side is brought into contact with the fixed contact pair. However, as the micro movable portion has flexibility, if the timing at which the attraction between upper electrode and the lower electrode on the right side is released comes after the timing at which the upper electrode and the lower electrode on the left side are attracted, both the moving contact on the right side and the moving contact on the left side are brought into contact with the fixed contact pair (see FIG. 1D in Japanese Unexamined Patent Publication No. 2006-190594), and a short circuit is caused between the a contact and the b contact. Therefore, in order to carry out switching between the right and left contacts quickly, it becomes difficult to control the timings for attracting and separating the upper electrodes and the lower electrodes on the left and the right sides, respectively.
Further, even if it is possible to provide the c contact structure, according to the micro contact switching device of Japanese Unexamined Patent Publication No. 2006-190594, as the fulcrum portion is provided at the center of the micro movable portion, it is necessary to wire the c contact around the fulcrum portion for a long distance. This can lead to a poor high frequency characteristic and inappropriateness for an application of switching high-frequency signals.
(Japanese Unexamined Patent Publication No. 2005-5267)
An MEMS switch disclosed in Japanese Unexamined Patent Publication No. 2005-5267 also has a structure such that an upper electrode and a lower electrode are attracted by an electrostatic attractive force between the upper electrode and the lower electrode, and a gap in a transmission line is switched using first and second contact portions provided for both ends of a supporting base supported in seesaw relation. According to this MEMS switch, the gap in the transmission line is closed by the contact portion on a side where the upper electrode is attracted to the lower electrode, and the gap in the transmission line on the other side is forcibly opened, and therefore reliability when opening the gap in the transmission line can be improved. Further, the transmission line is configured to form the c contact structure.
However, according to this MEMS switch, the first contact portion and the gap therebelow (the a contact and the c contact) and the second contact portion and the gap therebelow (the b contact and the c contact) are distant in both sides with the supporting base therebetween. Therefore, the c contact is wired for a long distance, resulting in a poor high frequency characteristic of the MEMS switch. Further, a movement stroke of the first and second contact portion is substantially equal to an end portion stroke of the supporting base when the supporting base swings, and it is not possible to increase the movement stroke of the first and second contact portion larger than this.
(Japanese Unexamined Patent Publication No. 2006-173132)
According to an MEMS switch disclosed in Japanese Unexamined Patent Publication No. 2006-173132, an inner actuating member and an outer actuating member are supported in seesaw relation above a substrate, and the inner actuating member is inclined to either direction by an electrostatic attractive force acting between the inner actuating member and the first or second fixed electrode on the substrate. The outer actuating member has a structure such that the outer actuating member is inclined in conjunction with the inner actuating member by being pressed by a pressure application rod of an inner swinging member, and the gap between a first and a second signal line is switched by a first and a second contact member provided on both ends of the outer actuating member. According to this MEMS switch, the gap between the first or second signal line is closed by the first or second contact member on a side where the inner actuating member is attracted to the first or second fixed electrode, and the gap between the first or second signal line on the other side is forcibly opened, and therefore reliability when opening the gap in the transmission line can be improved.
According to the MEMS switch having a structure as described in Japanese Unexamined Patent Publication No. 2006-173132, a portion of the signal line can be configured as the c contact structure by connecting one contact of the first signal line and one contact of the second signal line.
However, even with this MEMS switch, as the first contact member and the gap therebelow (the a contact and the c contact) and the second contact member and the gap therebelow (the b contact and the c contact) are respectively positioned at the ends of the outer actuating member, the c contact is wired for a long distance, resulting in a poor high frequency characteristic of the MEMS switch. Further, the movement stroke of the first and the second contact member is substantially equal to an end portion stroke of the outer actuating member when the outer actuating member swings, and it is not possible to increase the movement stroke of the first and second contact portion larger than this.
(Japanese Unexamined Patent Publication No. 2005-216552)
A micro relay disclosed in Japanese Unexamined Patent Publication No. 2005-216552 is such that an armature is driven using an electromagnet. Specifically, according to this micro relay 11, as shown in FIG. 1, both end portions of a thin film 13 of a base substrate 12 are respectively provided with pairs of fixed contacts 14a, 14c and 14b, 14c. An electromagnet 15 is contained within a hollow portion provided in the base substrate 12 at a lower surface of the thin film 13. On an armature block 16 provided over the base substrate 12, the armature 17 is rotatably supported to a frame portion 19 by projecting pieces 18 provided on both side surfaces of an armature 17, and moving contact base portions 20 provided for both end portions of the armature 17 are supported to the armature 17 by compression spring portions 21. Then, when the armature block 16 is provide over an upper surface of the base substrate 12, a moving contact of a lower surface of one of the moving contact base portions 20 faces the fixed contacts 14a, 14c, and a moving contact of a lower surface of the other of the moving contact base portions 20 faces the fixed contacts 14b, 14c. 
According to the micro relay 11, when the electromagnet 15 is excited, one of the end portions of the armature 17 is attracted to the electromagnet 15 depending on the polarity at that time, thereby causing the armature 17 to be inclined. Then, the moving contact of the lower surface of the moving contact base portion 20 positioned on the attracted side closes one of the fixed contacts 14a, 14c and the fixed contacts 14b, 14c. 
According to the micro relay 11, the fixed contacts 14c, 14c on the both ends are connected through the side of the thin film 13 to form the c contact structure. However, as shown in FIG. 2, the fixed contact 14c as the c contact extends over substantially an entire length of the base substrate 12, the high frequency characteristic of the micro relay 11 becomes poor and it is hard to design for the high-frequency application. Further, in the micro relay 11, the movement stroke of the moving contact (the moving contact base portion 20) is substantially equal to an end portion stroke of the armature 17 when the armature 17 swings, and it is not possible to increase the movement stroke of the moving contact larger than this.
(Japanese Unexamined Patent Publication (Translation of PCT Application) No. 2006-523001)
An electromagnetic relay 31 disclosed in Japanese Unexamined Patent Publication (Translation of PCT Application) No. 2006-523001 has a structure such that, as shown in FIG. 3, a contact element supporting body 33 in a leaf spring shape, a contact terminal 34, and an electromagnet (not shown) are layered on a printed circuit card 32. As shown in FIG. 4, conductor paths 35a, 35b, and 35c are formed on an upper surface of the printed circuit card 32, and the conductor paths 35a and 35b are disposed on right and left sides of an end portion of the conductor path 35c. A base portion of the contact element supporting body 33 is flexed, a pair of flexible arms 36 and 37 extends from the base portion, and a contact element 38 is provided on a lower surface of a tip end portion of the flexible arms 36 and 37. The contact terminal 34 is rotatably supported by an axis 39 so that the right and left portions of the contact terminal 34 swing up and down, and it can be switched between a state in which the right portion is lowered and a state in which the left portion is lowered, by the electromagnet. Then, when the left portion of the contact terminal 34 is lowered, a projecting portion 40 of the flexible arm 36 is pressed by the contact terminal 34 and a tip end of the flexible arm 36 is lowered, and the conductor paths 35a and 35c are closed therebetween by the contact element 38. In contrast, when the right portion of the contact terminal 34 is lowered, the projecting portion 40 of the flexible arm 37 is pressed by the contact terminal 34, and a tip end of the flexible arm 37 is lowered, and the conductor paths 35b, 35c are closed therebetween by the contact element 38.
As the electromagnetic relay 31 has the c contact structure and a length of the conductor path 35c as the c contact is made short, the electromagnetic relay 31 is appropriate for the high-frequency application.
However, with the structure of the electromagnetic relay 31 according to Japanese Unexamined Patent Publication (Translation of PCT Application) No. 2006-523001, the contact terminal 34 is driven by the electromagnet, and the flexible arms 36, 37 of the contact element supporting body 33 are moved by the contact terminal 34, thereby switching the contacts (the conductor paths 35a, 35b, and 35c). When a driving portion is configured by two members (the contact element supporting body 33 and the contact terminal 34) as described above, assembly accuracy and the like of the electromagnetic relay 31 decreases, carrying out a correct relay operation becomes difficult, and downsizing of the electromagnetic relay 31 becomes difficult. Further, according to this electromagnetic relay 31, as the movement stroke of the moving contact (the contact element 38) is substantially equal to a stroke of a free end of the flexible arms 36, 37, it is not possible to increase the movement stroke of the moving contact. Further, as a dissociating force of the moving contact is only an elastic restoring force of the flexible arms 36, 37, it is not possible to use for an actuator that needs the dissociating force of the moving contact.
(Japanese Unexamined Patent Publication No. 2002-254399)
FIG. 5A is a plan view illustrating a mirror device of the conventional example, FIG. 5B is a cross-sectional view taken along a line X-X in FIG. 5A, and FIG. 5C is a cross-sectional view taken along a line in Y-Y in FIG. 5A. A mirror device 41 in the figure is such that a mirror 43 in a disc shape is disposed horizontally above a substrate 42, and both ends of the mirror 43 are supported by springs 44 that are meanders in a zig-zag manner. Lower electrodes 45 are provided on both sides of the line segment that connects the springs 44 on an upper surface of the substrate 42 so as to face a lower surface of the mirror 43, and upper electrodes 46 are formed on the lower surface of the mirror 43 that faces the lower electrodes 45. According to the mirror device 41, when a potential difference is applied between the upper electrodes 46 and the lower electrodes 45 on either side, the potential difference applied upper electrode 46 is attracted to the lower electrode 45 to cause the mirror 43 to be inclined. An example of such a mirror device includes the one disclosed in Japanese Unexamined Patent Publication No. 2002-254399.
In order to increase the electrostatic attractive force between the upper electrode 46 and the lower electrode 45 for the mirror device 41 of such a structure, an inclination of a surface on which the upper electrode 46 is provided can be reduced, and the mirror 43 can be disposed closer to the substrate 42. In this case, however, an inclination of the mirror 43 is limited and becomes smaller. In contrast, in order to increase the inclination of the mirror 43, the inclination of the surface on which the upper electrode 46 is provided can be increased, or the mirror 43 can be disposed away from the substrate 42. In this case, however, as a distance between the upper electrode 46 and the lower electrode 45 increases, the electrostatic attractive force for inclining the mirror 43 becomes small. Therefore, it is difficult to increase the inclination of the mirror 43 with the mirror device 41 of this type.